This revised application requests continued support for a program of empirical and theoretical research on speech perception and spoken word recognition. The major goal of this project is to understand and describe how spoken words are recognized and how acoustic-phonetic information in the speech signal interacts with other knowledge sources to support spoken language understanding. The proposed research will involve behavioral studies of perception, memory and learning with normal-hearing adults and hearing-impaired children with cochlear implants and computational analyses of words in the mental lexicon using large computerized lexical databases to gain new knowledge about the perceptual and cognitive processes that human listeners use in perceiving spoken words and sentences. The proposed studies are organized into four major research projects: (1) spoken word recognition and the mental lexicon; (2) sources of variability in speech perception; (3) perceptual learning and adaptation; and (4) individual differences and working memory. The results from this project not only have important implications for understanding speech and language processing in normal-hearing and hearing-impaired adults but the basic research findings will also contribute to developing a much stronger theoretical basis for understanding and explaining the enormous individual differences in speech and language outcome measures in prelingually-deaf children who have received cochlear implants.